1. Field of the Invention
This invention pertains to the measurement of temperature using optical techniques and more particularly relates to an apparatus for determining temperature utilizing a sensor material having a thermally dependent refractive index.
2. Description of the Prior Art
Present technology utilizes thermistor beads having a temperature dependent resistance characteristic, wherein the thermistor's resistance is monitored to yield an indication of temperature. Such sensors, however, suffer from various disadvantages including susceptibility to electromagnetic radiation interference and the noise produced thereby. Furthermore, the flow of sensing current through the thermistor element may cause a temperature rise in the sensor, thus rendering such sensors inaccurate. These sensors are also bulky, slow responding, and costly to produce.
Optical sensors have the advantage of being relatively insensitive to electromagnetic interference as well as being small in size and adaptable to inexpensive manufacturing techniques. Optical sensors known in the art include birefringent digital temperature sensors which exploit temperature dependent birefringence effects of various crystals. In such a sensor, a source spectrum is transmitted by a fiber bundle through a polarizer. The polarization vector of the resulting light is then rotated by the birefringence cell through an angle which is dependent upon the temperature. A second polarizing filter is then used to convert the polarization changes into intensity changes. Such a sensor, however, requires the use of costly birefringent crystals and has a limited dynamic range. A further optical temperature sensor known in the art exploits the temperature dependent phosphorescence decay time of phosphors. In sensors of this nature a phosphor bonded to one end of a fiber optic light guide is illuminated with pulsed laser light. By examining the decay time of the phosphorescence emitted by the phosphor, a temperature measurement may be made. Such a sensor, however, requires complex electronics and has a slow response time.
The present invention provides a compact, simple, and economical apparatus having fast response for measuring temperature at remote and non-remote locations.